The present invention relates to the field of industrial painting and coating. More particularly, the invention relates to a method and system for controlling a reciprocating coating apparatus.
Reciprocating coating machines have been in wide use in the coating industry for a number of years. In general, a reciprocating coating machine has at least one arm and at least one applicator, one example being known as a paint spray gun, attached to the arm. The arm travels in a linear path (e.g. left/right, up/down, etc.) and typically is actuated by a motor-cam assembly or a pneumatic system. As the arm is in motion, the applicator is energized by a solenoid or equivalent device, and the applicator emits a mist of paint or other coating material. The area coated by the reciprocating coating machine is determined by the stroke of the arm and the width of the mist. An object, such as a tool or a machine part, is placed on a conveyor system and passes by the reciprocating coating machine. As the object travels past the machine, it passes through the mist and thus is covered by a coat of paint.
Since the range of arm motion in a reciprocating coating machine is typically designed to cover various part sizes, early reciprocating coating machines tended to be very inefficient. This was due to the fact that on early machines, the arm stroke was generally not adjustable. Thus, for example, if the part size encompassed the entire stroke of the arm, the coating application was fairly efficient. If, however, the part size was significantly less than the stroke of the arm, a significant amount of coating was wasted as the arm traveled through an area that did not require a coating (a dead zone). Furthermore, the excess stroke introduced a delay as the arm traveled through the xe2x80x9cdead zonexe2x80x9d and thus reduced the maximum speed the part could travel past the coating arm. Moving the part too fast could result in the part leaving the reach of the applicator, resulting in an uneven coating application or possibly uncoated portions of the part.
Attempts have been made to increase the efficiency of the reciprocating coating machine, and in particular, to reduce the waste of the coating material. One issue which has been addressed is the stroke of the coating arm. As discussed above, if the part size is significantly less than the stroke of the arm, a significant amount of coating is wasted. To solve this problem, adjustable cams were installed to allow the stroke to be altered. To change the stroke, the cam would be changed to meet the requirements of the part. Another solution was to use pneumatics to control the stroke. Pneumatic switches were placed at the desired upper and lower stroke points and when the arm triggered these switches, the air flow was reversed and the coating arm would change direction.
While these approaches address the problem of coating waste due to excessive stroke, they have their limitations and drawbacks. For example, it is impractical to have a cam on hand for every conceivable stroke length. Therefore, a cam is used that places the stroke length in the xe2x80x9cball parkxe2x80x9d for a particular part. Thus, while the stroke length may be reduced by the selected cam to more closely match the respective part, there is room for further improvement. Furthermore, the shape of the cam inherently has an arc in its swing, especially at the location at which the coating arm changes direction. Therefore, the motion of the coating arm is non-linear or of non-uniform speed, especially at the extreme stroke points. Yet another drawback of a cam-driven coating arm is that the center point of the stroke is difficult to change; additional cams are required to alter the center point of the stroke.
As mentioned above, pneumatic driven reciprocating coating machines employ pneumatic switches to set the arm upper and lower stroke travel. Thus, while the switches provide operator control of the stroke length, they must be set each time a new stroke length is desired. Once set, the switch positions need to be verified, and more often than not, re-adjusted until the desired travel is achieved.
Furthermore, changing the stroke on both the cam and pneumatic driven reciprocating coating machine requires that the production line, for example, be shut down while the adjustment is made. This results in significant down time and lost production. Another drawback is that the stroke length may not be changed dynamically e.g. xe2x80x9con the flyxe2x80x9d, to match the contour of a part passing by the coating arm.
Accordingly, it would be advantageous to facilitate adjusting the stroke length of a reciprocating coating arm. Additionally, It would be advantageous to facilitate adjusting the stroke center point of a reciprocating coating arm. It also would be advantageous to facilitate adjusting the stroke speed of a reciprocating coating arm.
In the light of the foregoing, one aspect of the invention relates to a coating system, which includes a coating applicator, a movable arm for moving the coating applicator to carry out a coating operation, and a dynamic controller for determining at least one of stroke length, stroke center point, and stroke speed.
A second aspect of the invention relates to a coating system, which includes a movable arm and at least one coating applicator coupled with respect to the movable arm. A first actuator provides motion to the movable arm, the first actuator being controlled by a computer controller. The computer controller includes a processor, and the computer controller is operatively coupled to the first actuator. A first data representing at least one of stroke length, stroke center point, and stroke speed of the movable arm is used in a computer program. The computer program is executed by the processor to cause the computer controller to dynamically command the first actuator to change at least one of stroke length, stroke center point, and stroke speed of the movable arm based on the first data.
A third aspect of the invention is a method for controlling a movable arm of a coating device. The method includes the steps of entering a first data into a computer controller, the first data representing at least one of stroke length, stroke center point, and stroke speed of the movable arm. A motion profile is generated based on the first data, and a position feedback indicative of the position of the movable arm is provided. A torque reference is produced based on the motion profile and the position of the movable arm, and is sent to an actuator to provide motion to the movable arm. The torque reference is regulated to dynamically move the movable arm to change at least one of stroke length, stroke center point, and stroke speed of the movable arm based on the first data.
Other aspects, features, and advantages of the invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating several preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention.